Many triggered spark-gap dischargers are known involving in addition to principal electrodes (cathode and anode) between which the principal electric discharge takes place, two "triggering" electrodes. One of these triggering electrodes is often constituted by one of the principal electrodes.
A DC voltage (20 kv for example) can be applied between cathode and anode, for example by connecting the cathode and the anode to the terminals of a capacitor charged by the DC voltage. When the voltage is less than the breakdown voltage between the cathode and the anode and greater than a threshold voltage which is a function (as is the breakdown voltage) of the geometrical disposition of the spark gap and of the nature and pressure of the gas surrounding the electrodes, a suitable electric discharge between the triggering electrodes is sufficient for triggering the principal discharge. For this purpose, an impulse is applied between these electrodes at a voltage of a few KV for example. An electric "triggering discharge" then takes place between these electrodes and triggers the principal discharge.
One use of the spark-gap discharger is that the energy of the triggering impulse can be very much less than that of the principal discharge.
It is very often important to be able to trigger the spark-gap discharger by means of an electrical impulse having not only little energy but also a small potential difference, e.g. less than 2 kilovolts. Various solutions have been proposed for this purpose:
One consists in reducing the distance separating these triggering electrodes, it being understood that from this view-point, there is an optimum distance which depends on the nature of pressure of the ambient gas and below which it is useless and harmful to descend. In the case of atmospheric-pressure spark-gap dischargers this distance is in the order of about 10 microns. Great triggering precision in terms of time requires this distance to be made with precision. Now, considering the insulation which must be provided between the triggering electrodes, the creation and maintenance of a distance as small as this poses difficult design problems.
For the same purpose, it is also known to occupy the space between the triggering electrodes with a solid dielectric. The triggering discharge then takes place on the surface of this dielectric. In effect, an electrical discharge -- preferably in a dielectric environment -- follows the interfaces between dielectics of different kinds and more precisely, in the disposition described, the interface between the solid dielectric and the gaseous dielectric. This boils down to saying that the voltage necessary for breakdwon is diminished. Nevertheless, if this voltage is to be very small, it remains necessary to give the solid dielectric separating the triggering electrodes a small thickness. This is why it has been proposed in French Pat. No. 7,033,577filed on Dec. 16, 1970, in the name of Compagnie Generale d'Electricite and in the corresponding U.S. Pat. No. 3,702,411, for a "Spark-gap discharger triggered in a gas" to provide this dielectric in the form of a thin sheet clamped between triggering electrodes which must be adjusted with precision.
Nevertheless, it remains desirable to simplify manufacture and to diminish further the triggering voltage without increasing the dispersion of the delay on triggering, i.e. the variations in the time which passes between the triggering pulse and the main discharge. The uncertainty of this delay is known as "jitter".
Preferred embodiments of the present invention provide a triggered spark-gap discharger having little dispersion of the triggering delay and a low triggering voltage while still involving only low production costs.